We present lattice results for the formfactors relevant in the K→p ℓnℓ and D→p ℓnℓ semileptonic
decays, obtained from simulations with two flavors of dynamical twisted-mass fermions and pion
masses as light as 260 MeV. For K →p ℓn decays we discuss the estimates of the main sources
of systematic uncertainties, including the quenching of the strange quark, leading to our final result
f+(0) = 0.9560(57)stat.(62)syst.. Combined with the latest experimental data, our value of
f+(0) implies for the CKMmatrix element |Vus| the value 0.2267(5)exp.(20) f+(0) consistent with
the first-row CKM unitarity. For D →p ℓnℓ decays the application of Heavy Meson Chiral Perturbation
Theory allows to extrapolate our results for both the scalar and the vector form factors
at the physical point with quite good accuracy, obtaining a nice agreement with the experimental
data. In particular at zero-momentumtransfer we obtain f+(0) = 0.64(5). A preliminary analysis
of the discretization effects is presented and discussed....more